The invention relates to an apparatus and method for use with controlling electrical potential of a downrigger wire line as used in fishing, in particular for relatively small downriggers as used by recreational fisherman.
It is well known that fish prefer to inhabit waters within specific preferred temperature ranges, and commonly water of the preferred temperature range is relatively deep, sometimes several hundred feet below the surface. In order to maintain a hook and a lure at that depth when trolling or mooching, a downrigger is commonly used, a typical downrigger being shown in patents of the present applicant, for example U.S. Pat. Nos. 4,044,968 issued August, 1977 and 4,932,602 issued June, 1990. It is not unusual for a small recreational fishing vessel to have two or more downriggers extending from different locations on its deck. Each downrigger has a heavy weight carried on a thin stainless steel wire line, the wire line being wound on a spool or reel. At least one fishing line with a lure and hook is releasably attached to the wire line using a downrigger release clip, which releases the fishing line from the downrigger wire line when the hook is taken by the fish. Downriggers are fitted with depth indicators for indicating length of the wire line extending from the reel, and thus if the length of unwound wire line is known, and the approximate depth of the weight is known, the approximate depth of the fishing lure will also be known.
Commercial trollers use more complex fishing gear, commonly called "gurdies", which use weighted lines to position fishing lures and hooks at known depths, but eliminate the release hooks of the recreational fisherman's downrigger. The gurdies have multiple reels to control multiple wire lines and associated weights, and a complex system of booms and pulleys are used to reduce the chance of the inadvertent fouling between adjacent fishing lines, wire lines, and weights.
It is well known that fish react to weak positive and negative electrical charges or fields in water, and it appears that some fish are attracted to a positive charge and are repelled by a negative charge. Attraction by the positive voltage charge is difficult to quantify, but even if the fish are not attracted by the positive charge, they are at least not repelled to the extent that they are repelled by a negative charge. Some fish showing the most sensitivity include salmon and trout, which are some of the most popular species of fish which recreational fisherman try to catch. If the downrigger is electrically insulated from the boat, a "natural" electrolysis between the stainless steel downrigger wire line and certain other dissimilar metals of the boat immersed in the water, e.g. a sacrificial zinc or aluminium anode, will create a natural positive voltage or charge around the downrigger wire line which can assist in attracting fish.
Commercial salmon trollers use an electrical potential controlling apparatus which accurately controls a resulting positive voltage on the wire lines associated with the gurdies. Because commercial fishermen use many wire lines, each wire line can be connected to the apparatus to create a complete zone of positive electrical potential around the boat. The electrical potential controlling apparatus used by commercial fishermen is sufficiently flexible and powerful to control voltage or potential of a few or many wire lines, and thus is unnecessarily complex and powerful for recreational fishermen who may use between one and four wire lines. Commercial fishermen usually wind the wire lines of the gurdies onto metal reels which are journalled on metal shafts mounted in housings on the vessel. It is usual to control the electrical potential on the wire lines by connecting an electrical cable to apply a positive DC voltage to electrically conducting structure associated with the gurdies, for example the axle or shaft mounting the reels, or the housings journalling the shaft. To use the apparatus correctly, the shafts and housings of the gurdies are insulated from the vessel.
In contrast, many downriggers used by recreational fisherman have plastic spools or reels, and consequently wire line carried on the downrigger reels cannot be electrically charged by connecting an electrical conductor to the reel axle. In addition, the wire line passes over a downrigger pulley which is also commonly made from plastic, and thus also insulates the wire line. Because of the difficulty of conducting electricity to the wire of the recreational downrigger, it has not been common practice to control electrical potential on downrigger wire lines of recreational fishermen's downriggers.